Electric fuse



June 10, 1941. F. s. KLEIN ELECTRIC FUSE Original Filed Aug. 6, 1937 INV EN TOR.

Patented June 10, 1941 UNITED STATE PATENT FFIQ Substituted forabandoned application Serial No. 157,288, August 6, 1937. Thisapplication May 15, 1939, Serial No. 273,383

10 Claims.

This invention relates to fuses which form a fusible link in an electriccircuit; when such fuses are opened, an electric are usually occurs andoften is maintained long enough to damage open fuse gaps, or fusecasings; and while a destructive arc endures, serious damage, evenpersonal injury progresses very swiftly where an accidental shortcircuit takes place.

It is generally understood that the ideal fuse is one in which themelting or volatilization of the link, i. e. a disruption, is prompt,brief, and with the minimum of violence; and such is the object of thisinvention.

In prior fuses many devices have been employed to limit an electric arc,and this seems to be the solution of the problem; such devices include,holding the link under tension, chemicals, parts which move to interruptthe arc, but an electric arc is swifter than any of these. Other devicesare pulverized material to smothe'r an are, or to crush a disruptinglink between two broad surfaces, but it is very often the nature of anelectric arc to persist in spite of such treatment; even in enclosuresproviding an indirect passageway for the link, an arc is prolongedthrough metallic vapor; but my new fuse is not to be confused with anyof the aforementioned nor with any device which utilizes the force of adisruption to break a once established arc, for I have provided apartition which stationarily blocks the path of an electric arc, beforeand during a disruption of the fuse link, without the least hindrance toa necessary disruption.

In this new fuse I use a link which may have end portions or othermembers of any description, but, at least one intermediate longitudinalsection which is a relatively short and more fusible part of the link,the purposes of that arrangement are well known and include localizing adisruption, which frequently is not realized because, by an inductiveoverload or short circuit between heavy metal bodies in slight contact,a very persistent are often consumes the entire link.

But I insure all the advantages of a short and particularly fusiblesection in a fuse link, by having an arc barrier of dielectric materialin the form of a plate, partition or substantially the same thing,secured transversely to the link, and tightly clamping and tightlyconfining only the middle part of said short section, which is the partmost susceptible to heat and the initiation of volatilization; and byhaving an end part of said short section extending from or clear of eachside of said Partition.

By this arrangement, fusing is retarded at the middle cross-section ofthe fusible section of the link, which prevents an electric are throughthe partition and allows only the end parts of that section to bedestroyed. Thereby resulting in an important feature of this invention,that is, the partition causes, simultaneously, two relatively small andwell separated ruptures in the fuse link, and prevents an are betweenthe remaining portions of the link.

The advantage of those two ruptures in the link is equal to the wellknown advantage of opening an electric circuit in two well separatedplaces simultaneously, that is, the damage that would result from asingle opening in that circuit is importantly reduced.

When my invention is made-up substantially as shown and described, thedamage and violence resulting in the link or the external circuit issuch as would scarcely be less with any other fusible device having thesame current carrying capacity.

The herein described partition, where it contacts the fuse link, is asthin, with respect to its breadth and the associated fuse gap, as ispossible for withstanding and preventing an arc, so as to leave a greatpart of the fuse link as free to be acted upon by excess current as anyfuse may be, and the partition may be of uniform thickness as the wordpartition usually implies; but I add thickness to parts of my partition,to provide body and surface for support or heat dissipation.

The invention above described can be used in any fuse gap whether openor inclosed, it is economical, simple, stationary, and constantlyblocking the path of an electric arc; only two end portions of thepurposely provided short section of my fuse link can be destroyed; whilethat short section may show incandescence when disrupted, such is notwhat I term an arc because it is necessary; the herein mentioned arc isto be understood as that unessential and destructive accompaniment of adisruption in a fuse which many have tried to eliminate.

In the instance of standard N. E. C. fuse gaps, open, or in casings,that part of my partition which grips a ten ampere link, need not bemore than one eighth of an inch in thickness, or, less than 15% of theone inch fuse gap, and 15% is also a suitable thickness for a partitionin a six inch six hundred ampere fuse gap. However, the spirit of thisinvention will be carried out if my partition is considerable thickerthan indicated,

providing the fusible section of my fuse link is correspondinglylengthened.

Much depends on the material used for the partition and a heatconducting material such as porcelain is preferred for absorbing heatfrom the link whereby a time lag is obtained to save a fuse link fromdisruption by an overload of current Which may subside; and to the sameend, a support is provided where the link is most susceptible toweakness from heat.

In the accompanying drawing, Fig. 1 is a view of a partly brokencartridg fuse showing the invention which is a partition forming an arcbarrier.

Fig. 2 is a view of the fuse link and separated parts of the arc barriershown at Fig. 1.

Fig. 3 is a sectional view of the arc barrier at Figs. 1 and 2.

Fig. 4 is a view of an arc barrier for open fuse links.

Fig. 5 is a crosssectional view of a screw plug fuse including aneconomical modification of the arc barrier shown above.

Referring in detail to the drawing, the number I indicates a fuse linkpreferably flat, having end portions at 2 and 2, and a longitudinallyextending intermediate section at 3 which, with respect to the endmembers, is short and more fusible.

At 4 is a partition forming an arc barrier which is clamped transverselyto the link, and tightly clamped so as to tightly confine only themiddle part of the fusible section 3 by means which provides a firm heatconducting contact with said middle part, whereby short portions of saidfusible section as at 5 and 5 extend free and clear of each side of saidpartition, the partition extending sufficiently in lateral directionsfrom the section 3 to block the usual path of an electric arc.

The partition may be composed of a plastic material and hardened on thelink, or made separate from the link; I prefer a porcelain partition,for its economy, with a concave surface on each broadside as at E and 5,thereby defining a relatively thin midsection I in the partition 4 andedges 8 of greater thickness for dissipating heat absorbed from the linkand for supporting th partition, furthermor said concave surfaces arefor reflecting metallic vapor away from a disruption in the link.

The partition 4 has two halves 9 and I0 joined edgewise and therewithclamping the middle part of the fusible section 3 in coaxial relationwith the partition. While the joined edges of the halves 9 and I I) maybe plain, I prefer to have the link passing through the partition in anindirect arc bafiling manner and I have made the juncture of the twohalves with a tongue and groove joint the tongue I! being on the half at9 and the groove I2 on the other half at IO.

In thus joining the two halves of the partition,

a triangular transverse ridge at I3 is formed in the middle of fusiblesection 3 to correspond with said tongue and groove, and in fuse linkscomposed of metal having insufficient pliability to be so deformed. itwill be necessary to preform the ridge I3 on the link. By thisarrangement the partition is readily secured in proper relation with thelink and the fusible section 3 clamped close in a tortuous arc bafflingpassageway.

Fig. 1 shows a cartridge fuse comprising, a tubular dielectric casingI4, having at each end a contact terminal I5 and I5 which may be of anytype, also a fuse link I attached to said terminals and a partition bothof which are arranged as described above.

At Fig. l the partition conforms closely to the cylindrical inside wallsof the casing so that the fuse link and partition as a unit can begently forced into the casing to frictionally hold in the properposition and clamped securely to the fusible section 3, this arrangementdivides the easing I4 into two combustion chambers at Iii and I6 with avery short length of the fusible section 3 on each side of the partitionor in each chamher. At Figs. 2 and 3 the partition and fuse link areshown in more detail.

Fig. 4 shows a fuse link I and a partition I arranged substantially asdescribed above, but for open fuse gaps; in this instance more porcelainis used in the partition, the better to dissipate heat especially whencopper links are used as they very often are hot for long periods.

At Fig. 4 the partition is generally rectangular in outline having, anupper half H, a lower half I 8, on a base I9, with holes 20 and 20 forfastening screws, also two threaded bolts 2| and 2| which extend atright angles from the base I9 and are slipped through holes in the twohalves of the barrier 4 to extend above the assembled whole and receivethe wing nuts at 22 and, 22 for clamping all together so as to easilyreplace any parts of the fuse link.

As shown, the middle part of a short fusible section 3 of the link I isclamped between the tongue II and the groove 52 which are on theadjacent edges of the two halves of the partition, again a relativelyshort portion 5 of the fusible section 3 extends out from each side ofthe partition-but because of the perspective'view at Fig. 4 the oppositeportion 5 does not show. This partition also has a concave surface 6 oneach side which is well adapted to reflect conductive metallic vapors inopposite directions when a disruption occurs on both sides of thebarrier.

Fig. 5 shows a screw plug fuse comprising, a dielectric casing I l whichpreferably is of porcelain or material which conducts heat well, theusual screw shell contact terminal 23, and bottom contact terminal 24, acombustion chamber I6 closed at the top by a cap 25 which includes awindow 26 of transparent material, a fuse link I such as described aboveand connected to the terminals 23 and 24.

At Fig. 5 the partition consists of a porcelain disc 4 which is wedgedin the combustion chamher so as to clamp only a middle part of thefusible section 3 of the link between the wall of the combustion chamberand the edge of the partition 4 and divide the combustion chamber intotwo consecutive compartments l6 and I 6 each of which contains a veryshort end portion of the fusible section of the link, and the two endsof that section is all that may be destroyed when the fuse blows.

With the invention described above, the factor of safety provided by anelectric fuse is materially increased by the prevention of unnecessarydestruction by an electric are when the fuse link is overloaded; and ashas been pointed out, the fuse link can often be saved when the heat ofan overload is only sufficient to weaken the link. Moreover the force ofgravity will have no effect on the link whatever its position may be.and the object of this invention is attained without in anywiserestricting a necessary disruption in the link, without strain on thelink, and with no dependence on any sequence of an overload of current.

This application is filed as a substitute for application No, 157,288,filed August 6, 1937.

I claim:

1. In the combination of a fuse link and a partition composed ofdielectric material stationed transverse to the fuse link; a fuse linkhaving an intermediate portion which forms a relatively short and morefusible part of the link, a partition tightly clamping and tightlyconfining only the middle part of said more fusible part of the fuselink and preventing an electric arc thereat, each end part of saidfusible part extending clear of said partition and therefore morereadily fused than the middle of said fusible part, whereby, excesselectric current is caused to produce, simultaneously, two separate andrelatively small ruptures of the fuse link.

2. In the combination of a fuse link and a partition composed ofinsulating material stationed transverse to the fuse link; a fusiblelink having an intermediate portion which forms a relatively short andmore fusible part of the link, a partition tightly clamping and tightlyconfining only a middle cross-section of said more fusible part of thefuse link, the thickness of the partition being such that each end partof said fusible part of the link extends from the partition into clearspace and fusing of said clamped middle cross-section of the fusiblepart of the link is sufficiently retarded to prevent an electric arcthereat whereby, a disruption of the fuse link is limited substantiallyto the two end parts of said fusible section.

3. In the combination of a fuse link and a partition stationedtransverse to the fuse link; a fuse link having end portions which formthe greater part of the link and a more fusible longitudinal sectionintermediate said end portions, a partition composed of heat conductingdielectric material, said partition tightly clamping and tightlyconfining only a middle cross-section of said longitudinal fusiblesection, the thickness of the partition in contact with said middlecrosssection of the fusible section being sufiicient to absorb heat fromthe cross-section and retard the fusing thereof While end portions ofsaid fusible section are being fused.

4. In the combination of a fuse link and a partition stationed incoaxial relation to the link; a fuse link comprising a fusible striphaving a relatively short intermediate portion thereof reduced incross-section and forming a more fusible portion of the strip; apartition composed of heat conducting dielectric material, saidpartition tightly clamping and tightly confining only the middlecross-section of said more fusible portion to retard fusing thereatWhile end portions of said more fusible portion are being fused, thelength of said more fusible portion being such that an end thereofextends clear of each side of said partition a sufficiently shortdistance to receive, when weakened by excess current, support from thepartition.

5. In the combination of a fuse link and a partition stationed incoaxial relation to the fuse link; a fuse link having a relatively shortand more fusible section intermediate less fusible longitudinalportions, a heat conducting dielectric partition comprising two parts,said two parts clamped edgewise together and therebetween tightlyclamping and tightly confining only a middle cross-section of said morefusible section, each end portion of said fusible section ex tendingclear of said partition.

6. In the combination of a fuse link and a partition stationed incoaxial relation to the fuse link; a fuse link comprising a fusiblestrip having a relatively short intermediate part thereof reduced incross-section and forming a more fusible section of the strip, apartition comprising two parts composed of heat conducting dielectricmaterial, said two parts tightly clamping and tightly confining only themiddle cross-section of said fusible section, and means to hold saidparts in position, the thickness of said two parts of the partition andthe length of said more fusible section being such that, sufficient ofthe fusible section is confined by the partition to retard fusing andprevent an electric arc thereat, while, end portions of said fusiblesection extend from each side of said partition and may besimultaneously fused, said end portions of the fusible section havingsufiiciently short length to receive, until melted by excess current,material support from said partition.

7. In the combination of a fuse link and a dielectric partitionstationed in coaxial relation to the fuse link; a fuse link comprising afiat strip of metal having a relatively short portion thereof reduced incross-section and located intermediate the ends of the strip, and havinga transverse ridge formed on the middle cross-section of said reducedportion of the strip; a partition comprising, a part having on an edgethereof a tongue, a part having on an edge thereof a groovecorresponding with said tongue, said edges of the two parts having athickness which is less than the length of said reduced portion of thestrip, clamping means to tightly clamp said two parts edge- Wise acrossonly the middle part of said reduced portion of the strip, and tightlyconfine said transverse ridge on the strip in a tortuous passage throughthe partition formed by the tongue and the groove, to prevent anelectric are therethrough the partition, and permit the ends of saidreduced portion of the strip to be fused simultaneously.

8. In the combination of a fuse link and a partition stationed incoaxial relation to the fuse link; a fuse link comprising a fiat fusiblestrip having a relatively short intermediate portion thereof reduced andforming a more fusible section of the link, a partition composed of heatconducting dielectric material, and having a relatively thin midsectiondefined by more thick edges on the partition for dissipating heatabsorbed from the midsection, said partition comprising, two half partshaving at the midsection of the partition a tongue on one part and agroove on the other part, means clamping said two parts together andtherewith tightly confining only the middle cross-section of saidfusible section between said tongue and groove, thereby forming atortouous passage adapted to absorb heat from said fusible section,prevent an electric arc, and permit both ends of the fusible section tobe fused.

9. In the combination of a fuse link, a casing therefor having contactterminal, and a partition stationed in the casing transverse to the fuselink; a fuse link comprising a fusible strip having a relatively shortsection thereof reduced in crosssection intermediate the ends of thestrip, a partition composed of heat conducting dielectric materialtightly clamping and confining only the middle cross-section of saidshort section of the strip, the thickness of said partition and thelength of said short section being such that the ends of the shortsection extend from opposite sides of the partition, and may be rupturedsimultaneously by excess current, and an electric arc prevented betweenthe ruptures.

10. In the combination of a fuse link, a tubular casing for the link,contact terminals on the 0215- the other of said parts, said thick edgesof the partition tightly holding to the inner sides of said casing, andthereby clamping and tightly confining between said tongue and saidgroove only :the middle cross-sectional portion of said relatively shortreduced portion of the fuse link, each end of said reduced portionextending clear of said partition for a short distance to cause,simultaneously, two separated ruptures of the link.

FRANKLIN S. KLEIN.

